In the Third Generation Partnership (3GPP) long term evolution (LTE), measurements take the wireless transmit/receive unit (WTRU) mobility state into account. For example, whether a WTRU is moving with low or zero speed has a different effect on the measurements than a WTRU moving with high speed on a rural area or a highway due to the Doppler Effect in the radio transmission and reception. Therefore in LTE, different scaling factors for measurements apply to the WTRU in different mobility states to balance or normalize the Doppler Effects on different mobility speeds. How to maintain the WTRU mobility states between Idle mode and Connected mode is not specified.
In LTE, the WTRU has three mobility states: low mobility, medium mobility, and high mobility. In Idle mode, when the WTRU does not have a call, it counts the number of reselections. In Connected mode, when the WTRU has a call, it counts the number of handovers. The WTRU counts the number of reselections or the number of handovers and determines whether it is not moving (also called stationary), it is moving slow (also called normal mobility), or it is moving fast (also called high mobility). Reselections and handovers are treated differently because the time needed to reselect is different from the time needed to perform a handover. The mobility states cannot be carried over from Idle mode to Connected mode for most purposes. A mechanism of adapting the mobility state when the WTRU transitions from Idle mode to Connected mode is needed. Also, the mobility state between modes should not be lost, meaning if the WTRU is moving fast while in Idle mode, and then transitions to Connected mode, the WTRU should not have to restart the mobility state determination. For example, if the WTRU is moving fast (i.e., in the high mobility state) it has an impact on how the WTRU performs reselections and handovers.
When the WTRU attempts to reselect to another cell, it needs to make sure that the target cell satisfies the minimum signal level, signal strength, and condition. The WTRU compares this data with some parameters that are transmitted by the network. That comparison is embodied in an equation called the S criteria. The S criteria effectively says how strong or weak the target cell is. If the S criteria, which is the difference between the signal strength and the threshold signaled by the network, is below zero, then the WTRU does not have to consider the target cell. If the S criteria is above zero, then the WTRU may proceed to camp on the target cell. The S criteria means that the signal strength of the target cell has to absolutely meet at least a minimum threshold, below which the network thinks that the target cell is not worth camping on. The LTE WTRU cell selection and reselection basic rules have the WTRU check the serving cell or another cell's signal strength using the S criteria. In LTE, one component in the S criteria, i.e., the Pcompensation parameter, remains undefined and needs to be specified.
LTE includes the concept of priority in cell reselection, which means that there are certain frequencies, for example, UMTS or GSM, that are given a priority. The WTRU has to follow the priority, so, for example, frequency “a” may be given priority one, frequency “b” may be given priority two, or vise versa. The WTRU has to make sure that it first tries to camp on frequency “a,” and if it cannot find the cell of frequency “a,” then it goes to frequency “b.” Currently, in the standards, there is no clear indication how long these priorities are valid. The WTRU may be signaled a priority using system information or dedicated RRC messages. But when the WTRU considers the priorities to no longer be valid or expired is not described.
In UMTS systems, there is a parameter called Pcompensation, which compensates for the pathloss when a WTRU performs cell reselection. There is no clear indication in LTE to date of how the Pcompensation parameter is going to be designed. This disclosure proposes some definitions of Pcompensation.